1. Field of the Invention
This invention relates to drill bits and power bits having a stepped, cylindrical coaxial construction for drilling holes of different diameters and more particularly to drill bits having a shank which provides for quick release securing of the bit to the chuck of a handle.
2. Background Art
Drill bits of a stepped construction have been used for providing holes of different sizes. The diameter hole desired depends on the depth of penetration of the drill bit into the material. For example, Oakes U.S. Pat. No. 3,758,222 and Korb et al. U.S. Pat. No. 4,582,458 each disclose drill bits having coaxial cylindrical surfaces with bevelled portions which extend between the cylindrical surfaces helically to provide axial clearance for the drill. At least one flute extends axially along the length of the cutting portion of the drill bit for providing a cutting surface.
Known disclosures of such drill bits have been mainly for use in fixed or portable drills. These drill bits usually have a shank that is cylindrical or cylindrical with up to three flats, the flats being spaced apart equally in order to prevent slippage. Such shanks are appropriate for use in a standard chuck to use with these drills. The chuck is tightened around the shank to hold the drill bit within the tool during use and the shank helps avoid slippage.
The connection into and tightening of the chuck around the drill bit shank is an unnecessarily time-consuming procedure and is occasionally prone to accidental misalignment of the drill bit from the axis of rotation of the drill chuck. This may result in further lost time in untightening the chuck, realigning the drill bit and retightening the chuck. Furthermore, if the misaligned drill bit is used in drilling, the workpiece may be damaged or the drill bit may break, which may result in serious injury to the operator.
More recently, hand tools and power tools have been manufactured utilizing a quick-change capability allowing swift, efficient and essentially error-proof insertion of tool bits without misalignment. For example, screwdriver tips or hexagonal bolt tips having a construction generally able to be quickly changed are known. Other tools have been used for quick change which are known in the industry as power bits. The term "power bit" refers to elements typically used for driving fastener devices such as screws, nuts, and bolts. To facilitate the quick change of these types of bits within power tools, such as hand held power tools that are driven by electric or air driven tools, various quick change devices have been utilized. For example, one type of a quick release device having a quick change capability is found in U.S. Pat. No. 4,184,692. This patent describes a quick release chuck similar in principle to most quick release chucks of power tools in present use. The American National Standards Institute has provided a specification for quick change tools, known as ANSI B107.4-1973, to standardize the shape, dimensions and other features of the shank of the tool bits to provide easy interchangeability of tool bits.
The known use of quick change devices in present use requires that the chuck for which these tools are intended for use have a specific construction. An example of such construction is taught by U.S. Pat. No. 4,692,073. The specific chuck construction is not of overriding importance to this discussion other than as an explanation of the use of the inventive drill bits within the context of hand held power tools.
What is not shown in the prior art and what is necessary for providing a quick change ability to drill bits of the conical shaped drill bits.